Hypopituitarism is a disorder where the pituitary does not secrete enough or any of one or more hormones. The literature varies on this, however. Some define it as "two or more hormones". However, the bottom line is the patient is deficient and this will affect one or more of the bodies functions. Panhypopituitarism, on the other hand, is the deficiency and/or total loss of all hormone production in the pituitary.
The pituitary gland is a bean-shaped (think lima bean) organ that is at the base of the brain. The gland anterior lobe, the intermediate lobe, the posterior lobe. The intermediate lobe is rudimentary in human beings but produces several hormones whose physiologic significance is only now being established.
The pituitary is attached to the hypothalumus (a part of the brain that affects the pituitary gland) by nerve fibers. The pituitary gland itself consists of three sections:
- growth hormone
- prolactin - to stimulate milk production after giving birth
- ACTH (adrenocorticotropic hormone) - to stimulate the adrenal glands
- TSH (thyroid-stimulating hormone) - to stimulate the thyroid gland
- FSH (follicle-stimulating hormone) - to stimulate the ovaries and testes
- LH (luteinizing hormone) - to stimulate the ovaries or testes
- MSH(melanocyte-stimulating hormone)- to control skin pigmentation
- ADH (antidiuretic hormone) - to increase absorption of water into the bloodby the kidneys
- oxytocin - to contract the uterus during childbirth and stimulate milk production. It is also believed to be important for orgasm
Not only are these hormone levels important, but the levels of other hormones affected by these are measured. In the thyroid, TSH from the pituitary affects the levels of T3 and T4.
In the adrenal gland, the level of cortisol is affected by the level of ACTH. It's that feedback loop I'm
"When Cortisol is a Night Owl" for more on this.
In post-pubescent females, FSH acts on the ovarian follicles to produce estrogens and LH is instrumental in the production of progesterone. In males, LH is instrumental in the production of testosterone. The hypothalamus secretes gonadotropin-releasing hormone (GnRH) to the pituitary gland in pulses. These, in turn, stimulate the pituitary gland to secrete luteinizing hormone (LH) which then stimulates the Leydig cells of the testes to produce testosterone.
That brings us to the hypothalamus. The hypothalamus is a region of the brain above the pituitary. It contains several types of neurons responsible for secreting different hormones. These are released into the blood in the capillaries and travel to the anterior lobe of the pituitary.
- Corticotropin-releasing hormone (CRH)
- Thyrotropin-releasing hormone (TRH)
- Growth hormone-releasing hormone (GHRH)
- Gonadotropin-releasing hormone (GnRH)
Altogether, these glands and their hormones comprise the Hypothalamic-Pituitary-Adrenal axis, also known as the HPA-axis. I have not touched on the adrenal hormones, yet, except to mention cortisol.
I will get there.